Ted Cruz is the best political tactician in the Republican race. He started his campaign by identifying a clear constituency—self-described “very conservative” voters—and acting as their undisputed champion. Before the voting ever began, Cruz, through superior fund-raising, compelling debate performances, and a bit of luck, drove three of the top competitors for this slice of the electorate—Rick Perry, Bobby Jindal, and Scott Walker—out of the race. In Iowa, the early state with the largest share of very conservative voters, Cruz proved similarly adept at the mechanics of politics. He used sophisticated micro-targeting to identify obscure local issues, such as a fireworks ban, that could win him small pockets of voters. He won the state by three points, and three more of his right-wing rivals—Mike Huckabee, Rand Paul, and Rick Santorum—departed.

Candidates like Cruz are not generally favored to win the Republican nomination. While Iowa’s Republican caucus is controlled by very conservative voters—specifically, conservative evangelicals—the state is an anomaly. In the past two fights for the Republican Presidential nomination, the Iowa winners, Mike Huckabee in 2008 and Rick Santorum in 2012, were knocked out of the race by their more mainstream conservative rivals. But Cruz has advantages that neither of those men possessed. He is a better communicator. His campaign is better funded, and, as the exit polls from New Hampshire suggest, the Republican electorate as a whole may have moved to the right since 2012, increasing the ranks of Cruz’s natural constituency.

But for all of Cruz’s tactical successes so far, he made one enormous mistake: he misunderstood the threat posed by Donald Trump. During a meeting with fund-raisers in December, Cruz explained his tactical approach to Trump and Ben Carson, and a recording of his comments subsequently leaked to the Times. “My approach, much to the frustration of the media, has been to bear-hug both of them, and smother them with love,” Cruz said. “People run as who they are. I believe gravity will bring both of those campaigns down, I think the lion’s share of their supporters come to us.”

Cruz was correct about Carson, whose campaign shows no life, but he was spectacularly wrong about Trump. By repeatedly praising Trump throughout 2015, Cruz did more than any other Republican to validate the reality-TV star as a true conservative.

At the CBS debate last night, Cruz tried desperately to undo that damage, and his attempt to unmask Trump as a closet liberal led to the most fiery exchange of the evening.

“You shouldn't be flexible on core principles,” Cruz said. “I like Donald, he is an amazing entertainer, but his policies for most of his life . . .”

Trump interrupted to take the compliment—“Thank you very much, I appreciate it”—but Cruz continued to prosecute his case: “For most of his life his policies have been very, very liberal. For most of his life, he has described himself as very pro-choice and as a supporter of partial-birth abortion. Right now today as a candidate, he supports federal taxpayer funding for Planned Parenthood. I disagree with him on that.”

Trump, who appeared irritated and testy throughout the evening and even lost a crucial exchange to Jeb Bush, looked like a red version of the Hulk when he responded. “You probably are worse than Jeb Bush. You are [the] single biggest liar,” he said, adding, “This guy will say anything, nasty guy. Now I know why he doesn't have one endorsement from any of his colleagues.”

Cruz, the former college debate champion, shrugged off the invective and laid a trap. “You notice Donald didn’t disagree with the substance that he supports taxpayer funding for Planned Parenthood,” Cruz said. “And Donald has this weird pattern, when you point to his own record he screams, ‘Liar, liar, liar.’ ”

Trump demanded to know when he ever said that he supported Planned Parenthood, and Cruz pointed viewers to a video in which Trump said just that. Oddly, Trump then repeated exactly what Cruz had accused him of saying: “It does do wonderful things but not as it relates to abortion.”

Trump is right. The majority of the services provided by Planned Parenthood have nothing to do with abortion. The group spends ninety-six per cent of its budget on services related to preventing sexually transmitted diseases, and providing contraception, cancer screening, and other women’s services. But, in a Republican primary, Trump might as well have opted to burn Ronald Reagan in effigy.

Trump’s liberal record has not been well-ventilated in the Republican race for two reasons. Cruz, the most well-funded conservative, stuck to his hug-Trump strategy until just a few days before the Iowa caucuses. Meanwhile, the candidates competing for more moderate Republicans have been busy attacking each other. But last night’s debate represented a drastic change in tactics for both camps. Cruz consistently attacked Trump as an ideological heretic on domestic policy, while Jeb Bush attacked him as out of touch with the G.O.P. on foreign policy. Just as Cruz got Trump to defend Planned Parenthood, Bush got him to partially blame 9/11 on George W. Bush, a statement that many liberal Democrats might agree with, but which is unpopular among Republicans, especially in South Carolina, where George W. is well-liked enough that Jeb will campaign with him on Monday.

And now there is a new accelerant to the Cruz–Bush campaign to turn Trump into a liberal: Antonin Scalia’s death. For many ideological conservatives, the makeup of the Supreme Court is the most important issue in America. Trump has won over voters who more naturally align with Cruz or Bush by emphasizing issues like immigration, political correctness, and a draconian approach to the war on terror. By doing so, he has cleaved the Republican electorate along class lines rather than ideological lines. The coming war over the Supreme Court could help reverse that.

The success of Cruz’s campaign may depend on that fight. “Don, the reason that principle matters sadly was illustrated by the first questions today**,”** Cruz told Trump, referring to Scalia’s death. “The next President is going to appoint one, two, three, four Supreme Court Justices. If Donald Trump is President, he will appoint liberals.”

If Republican voters don’t end up buying Cruz’s argument, even after the renewed attention to conservative principles in the eulogizing of Scalia, he will have nobody to blame but himself.

Ryan Lizza is the Washington correspondent for The New Yorker, and also an on-air contributor for CNN.